The driving device applies an ejection pulse signal and an auxiliary pulse signal as drive signals to the share mode type inkjet head. The ejection pulse signal drives the actuator in such a way that a drop of ink (ink drop) is ejected from a nozzle. The auxiliary pulse signal drives the actuator to such an extent that no ink is ejected.
There is a multi-drop driving system as an inkjet head driving system. In this driving system, one pixel is formed with one to plural ink drops, thus expressing gradation. The driving device continuously outputs an ejection pulse signal to the actuator by the number of drops corresponding to the gradation value of the pixel. Also, in order to generate preliminary vibration of the actuator, the driving device outputs an auxiliary pulse signal immediately before the ejection pulse signal for the first drop. Such an auxiliary pulse signal is referred to as a boost signal (BST). Alternatively, in order to absorb the vibration of the actuator after ink ejection, the driving device outputs an auxiliary pulse signal immediately after the ejection pulse signal for the last drop. Such an auxiliary pulse signal is referred to as a dump signal (DMP).
In the share mode type inkjet head, an actuator is shared between adjacent ink chambers. That is, ink chambers that are not at the ends of the head share have a first actuator shared with an ink chamber adjacent thereto on one side, and a second actuator shared with an ink chamber adjacent thereto on the other side. Therefore, when an ink drop is ejected from a nozzle communicating with the ink chamber concerned, the one actuator shared with the ink chamber concerned in the adjacent ink chambers on both sides of the ink chamber concerned is actuated as well. At this time, if the other actuator is also actuated in the two adjacent ink chambers, the ink may be ejected erroneously. Thus, the driving device needs to drive the two ink chambers sharing the other actuator, simultaneously with the same electric potential so that the other actuator is not actuated.
In this way, the driving device outputs a drive pulse signal synchronously with an ejection pulse signal also to the ink chamber communicating with the nozzle that does not eject ink drops. Meanwhile, the driving device properly outputs an auxiliary pulse signal to the nozzle that does not eject ink drops. Therefore, the driving device can only output an auxiliary pulse signal in a section that excludes a section where the drive pulse signal must be outputted, from one cycle of the ejection pulse signal.